There are known self-extinguishing polymeric compositions wherein the retarding component consists of organo-brominated compounds synergistically associated with antimony derivatives, bismuth derivatives or tungsten derivatives (see R. Gachter et al "Plastics Additives Handbook"--Hanser Pub.--Munich, pages 539-541 (1987)).
Nevertheless, particularly in the case of antimony, which, besides, is the most broadly used component, there are some problems to be solved, in particular as regards the availability and the costs and, from the technical-application viewpoint, a not always satisfactory dispersibility in the polymeric mass, and the toxicity.
The present invention offers an alternative solution as it permits a substitution of the antimony derivative or of an equivalent derivative, the global retarding effectiveness being substantially equal or even improved.
On the other hand it is known to use zeolites or molecular sieves (see Jpn. patent applications Kokai Tokkyo Koho JP 63/92661 and Kokai Tokkyo Koho JP 63/170440), however not associated with other components of the self-extinguishing system, in order to impart to the articles a higher thermal stability and a more effective control of the flue gas emission during combustion. The present invention differentiates owing to the presence of a synergistic effect between zeolite and organic halogen-derivative (bromo-derivative) and owing to the presence of a modifier of the polymeric structure at the pyrolysis temperature.
U.S. Pat. No. 4,070,315 describes, for the ABS resins, an additive based on halogen-derivatives and magnesian bentonite, the latter having a synergistic action in the place of antimony. However, this solution is conceptually different from the one disclosed in the present invention since the bentonite has a chemico-physical nature substantially different from the one of the zeolites and furthermore it is not modified and/or associated with other substances; moreover, the cited patent lacks the concurrence of the polymeric structure modifying system, which is an essential part of the present invention, as better defined hereinafter.
The association of molecular sieves with organic halogenated flame retardants for SBR rubbers is the object of German patent DD 242618, where the following advantages are specified: stability during processing of the formulations and achievement of a higher retardant concentration. Also in this case no synergic effects are cited; neither is use made of organic activating reactive systems acting as modifiers of the polymeric structure at the pyrolysis temperature. U.S. Pat. No. 3,829,400 describes the use of calcium, zinc and magnesium bromides for the external fire-proof treatment of polyamide fibers. However it is not known that inorganic halpolyamide ides have been recommended as components of thermoplastic polymeric formulations with a specific antiflame function. Even the introduction of inorganic halides into such formulations encounters serious hindrances due to a difficult dispersion. However, neither associations of inorganic halides with substrates suited to allow the dispersion in polymeric masses are described in the prior art.
Last, U.S. Pat. Nos. 3,441,524 and 3,420,786 illustrate the use of radicals-generating activators, for example of the type described in U.S. Pat. No. 4,666,947, in combination with organic bromo-derivatives, in order to impart flame-retarding properties to styrene polymers. In this case, a viscosity decrease and a consequent dripping effect can be observed.
Nevertheless it is not described the association of such radical activators with cross-linking compounds, according to the present invention, in order to give rise to a contrary behaviour, namely to an increase in the viscosity of the polymeric matrix and to the subsequent formation of a cross-linking mass which, thanks to an intimate connection with the zeolitic substrate, represents a surprising flame-extinguishing effect, which is superior to the one obtained by pyrolytic dripping.
Thus, it is an object of the present invention to provide self-extinguishing polymeric compositions, based on organic halogen-derivatives and on adducts of zeolites modified with inorganic halides, which are free from the drawbacks discussed hereinabove in connection with the prior art.
Another object consists in providing compositions which are substantially free from components based on antimony, bismuth, tungsten and/or based on aromatic halogen-derivatives etc., which are potentially toxic. Conversely, there are used more reactive halogen-derivatives, such as hexabromo-cyclododecane, which do not involve potential toxic effects due to the formation of dioxines or of furans during combustion, especially in the presence of antimony.
Still a further object is to provide an antiflame system for self-extinguishing polymeric compositions, which is capable of securing a high antiflame activity in all the main polymer types (polyolefins, polyesters, polyamides, etc.) differently from the known antiflame systems which selectively exert their effective action with respect to one polymer class or to few polymer classes.
Lastly, a further object is to provide self-extinguishing compositions without dripping phenomena at the pyrolysis temperature.